A Redox-Active Phenothiazine-based Pd₂L₄-Type Coordination Cage and Its Isolable Crystalline Polyradical Cations

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Polyradical cages possess intriguing physical and chemical properties.
• Challenges exist in the synthesis and characterization of polyradical systems.
• Coordination cages offer a platform for constructing complex molecular architectures.

Purpose of the Study:

• To synthesize a polyradical cation cage through post-synthetic modification.
• To investigate the redox activity and properties of the synthesized polyradical cage.
• To establish facile methods for the synthesis and characterization of novel polyradical systems.

Main Methods:

• Post-synthetic oxidation of a phenothiazine-based Pd2L4-type coordination cage.
• In situ UV/Vis-NIR and EPR spectroelectrochemistry for electrochemical oxidation studies.
• EPR and NMR spectroscopies for monitoring chemical oxidation and reduction.
• Single crystal X-ray diffraction for structural analysis.
• Magnetic susceptibility measurements.

Main Results:

• Successful synthesis of a polyradical cation cage (1^4•+) via oxidation of coordination cage 1.
• Demonstrated reversible electrochemical and chemical redox activity of cage 1 and 1^4•+.
• Isolated and characterized 1^4•+ using X-ray diffraction, revealing distinct electronic structure and conformation.
• Identified predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 1^4•+.

Conclusions:

• A facile synthetic route to polyradical cation cages has been developed.
• The study provides insights into the synthesis and characterization of novel polyradical systems.
• The findings open new perspectives for the development of functional supramolecular cages.